The multiverse runs on thought, and belief. Every sentient being, whether it’s an ant, an elf or a djinni, posesses a soul and a spiritual presence. The soul’s power is personality and belief, which can reshape the multiverse itself. When belief and worship (or fear) is directed, it flows into the object of belief and gives it power. When the people of the swamp believe that the trees are watching over them and want offerings, it will eventually become true if enough people believe it. The vast majority of thoughts and emotions, though, flow directly into the collective unconsciousness of the multiverse; an untapped sea of wild magic known to sorcerers as the Astral Plane.

Mortal creatures have bodies made of crude matter, which are vessels for the soul. They tend to have little innate magic, but are protected by their own mortality; when a mortal creature dies, the soul is released and passes on to the afterlife. For a spiritual creature, on the other hand, their soul is their body. Their “body” is made of their own spiritual power, and they can be very powerful as a result. If it is damaged or destroyed, however, that being may cease to be.

The true shape of reality is as complex as the minds responsible for it; it is not trivial to neatly separate. Nonetheless, this is exactly what scholars of the planes attempt to do when they speak of “the planes” or “the great wheel”.

The Elemental

While some scholars depict the elemental planes as neatly differentiated and uniform in nature, the truth is that they are chaos. They are a primordial mess of unformed creatia that bleed into each other in many pockets and bubbles. They are inhabited by many strange entities, the oldest of which are the elementals - spirits of pure elemental affinity that can survive only when inhabiting their element. Some scholars believe that the elemental planes are the seed from which the universe grew, and that the elementals and their kin are the oldest spirits of all.

A student of the elemental planes should not make the mistake of thinking that their chaotic and formless nature makes them beyond comprehension. Though it is true that they are always in motion, some areas are less unpredictable than others; some parts of the Elemental remain stable for centuries at a time. Pockets of the Elemental can be like little worlds unto themselves; those who dwell in them are usually aware of other pockets and bubbles, and how to get to them.

Here is an example of an elemental journey, to illustrate the point:

The Material

The material planes are dimensions which have been elevated from the elemental chaos, the real and mundane worlds in which mortals dwell. Their ultimate origin is unclear. Some believe they formed naturally, while others claim they must have a guiding hand. Those who serve a god, of course, are wont to say that their deities are the architects of the world. Others believe that one of the ancient elemental races - such as the genies - must have been responsible.

Most material worlds only encompass a single star system - at their boundaries is a veil that the mortal eye perceives only as inky void. Those who have come close in Spelljammers, though, describe that boundary as a shimmering curtain of rainbow colours that leads into the Ethereal Plane. This isn’t the only place that the material planes are connected to other realms. Natural portals to the elemental planes have a way of forming on the Material; in the heart of a volcano, the ocean floor, or the Underdark for example.

What, then, of the stars in the night sky? They can be many things. Some are distant material worlds, viewed dimly through the veil of the Ethereal. Others may be pocket planes, bubbles of stability that float in the elemental chaos. Some are even further away - the outer planes, where deities dwell. It is believed that the gods only take their place in the night sky if their power in the world is great enough to give them a foothold there. Perhaps this is why the stars are said to grow and fade with time.

The Border Ethereal

Until now, we have spoken only of the planes of crude matter - whether unformed and chaotic, or with stability and shape. However, there is a world, too, of spirit. It lays over the Elemental and Material alike, yet is rarely felt by those who dwell there. If a person’s body resides on the Material, the Ethereal is where the soul dwells. It is split by scholars into two parts: likening it to an ocean, the Border Ethereal is the shore and the Deep Ethereal is uncharted water.

The Border Ethereal is a pale reflection of the waking world, and is the home of discorporate spirits and restless shades. In most places, it seems no different to the “real world” viewed through a washed-out lens. Visitors to the border can pass amongst the living and through solid matter, and they will not be seen or felt by those around them. Spend time in the border, though, and you’ll realise all is not as it seems. Thoughts and emotions have a real reverberation there - and places of strong emotion or negative energy can transform the appearance and reality of a place in the border. Like attracts like, and such places can be dangerous - for they can attract dark spirits and negative energies.

Of course, those who wish to pass deeper into the Ethereal must seek out those very places that most travellers are warned to avoid. Places of great emotion, sites of natural power, the locations of wondrous or terrible deeds, or sacred places - these are the places where the border least resembles the waking world, and where the veil is the thinnest. In these places that have been twisted and made strange by the echoes of thought and memory, it is possible to “cross over” and enter the spirit world proper - the Deep Ethereal.

The Deep Ethereal

The Deep Ethereal lies beyond the border - it is not merely a reflection of the physical world, but the manifestation of the subconscious emotions and thoughts of all sapient beings. In some places, the Deep Ethereal resembles the real world writ large - a towering labyrinthine city or a forbidding forest of enormous trees that is both alienating and unsettlingly familiar, for example. In other places, it may be a world of mirrors and shadows, a twisted place where dark spirits and dark emotions are let loose to prey on the living.

Deeper into the Ethereal, your surroundings may be beyond mortal comprehension entirely - you may see a tavern filled with weary travellers simply because your brain cannot process the truth of your surroundings. In truth, there is no tavern, and the weary travellers are spirits - the native inhabitants of this strange realm that does not operate on the laws of the natural world. As one ventures deeper, both time and space are increasingly in flux and the laws of reality become guidelines that are easily cast aside.

The deeper one travels into the spirit world, the less stable it becomes. Nearer the shores, the Deep Ethereal is still close to being a true reflection of the waking world. It may be distorted and strange, but it is still recognisable and navigable. As one draws closer to the Astral Plane, however, the thoughts and feelings that shape the world around you become more fluid and abstract. It no longer reflects consistent, sensible concepts - instead, it veers into the troubled and scattered impressions of the schizophrenic mind. One who chooses to seek out this strangeness, instead of avoiding it, will walk the left-handed path that eventually leads into the realm of unconstrained thought - into the Astral.

The Astral

The Border Ethereal is the shore, and the Deep Ethereal is uncharted water. If this is true, then the Astral is what lies beneath the waves and in the ocean depths. It is the source of all magic, a formless and chaotic maelstrom of psychic energy endlessly fed by the thoughts, desires and dreams of all beings. Whereas the Deep Ethereal is merely a reflection of thoughts and emotions, the Astral is a place where the difference between “being” and “imagining” is nil. This can make it a realm of infinite wonder, but also one of terrible danger to those who dare expose their mortal bodies to it.

The very substance of the Astral is thought, emotion and belief made real and given shape and form. This psychic maelstrom means that reality around you is constantly shifting and changing: it’s like a thousand voices are all shouting over each other, each asserting that reality is this or that. The environment and the laws of reality change from moment to moment. Sentient beings appear from nothing, born from the collective unconsciousness of the multiverse - and disappear just as quickly. At least, that’s how it is in the most chaotic regions, where the astral storms rage so powerfully that no individual thoughtform can survive.

Most visitors to the Astral will only end up in such places by accident or mishap. The Astral isn’t just chaos; there are are quiet spots where the environment is relatively stable - where you can catch your breath. There are places where, instead of formless chaos, there is some disjointed level of reality that asserts itself - such as in the Dreamlands, where sleeping minds drift and build worlds out of thought in the Astral.

The bodies of dead gods, which drift through the mists, are another common destination. The remnants of the deity’s will makes the Astral stable enough that many are home to outposts of mages and scholars. After all, the Astral is the source of all magic - it’s like an enormous ley-line that surrounds you in every direction, providing the perfect place to perform great works. Filled as it is with thought and emotion, it’s also like an enormous library that contains every book ever written - if only you have the means to sift through it. Places of stability are also a popular place to hide things - and where treasures are hidden, you’ll find treasure hunters.

Most mortals that visit the Astral, however, do so in the form of a projection - far safer than risking your physical form - and they have specific locations in mind. Even for them, travel in the Astral is often confusing and difficult. It has nothing to do with distance or landmarks, but with feelings. Travel in the Astral can be frustrating, going in nonsensical circles endlessly without fruit, or it can be very sudden - you open a door or climb a cliff, and suddenly your objective is before you. It’s closer to solving a riddle than making a journey.

The Outer Planes

In the vast chaos of the Astral, there exist places of relative calm and stability - such as the corpse of a dead god, the dreams of a sleeping mind, or even the domain of a powerful spirit or order of ascetic monks that can calm the turbulent thoughts that surround them. However, such feats are child’s play compared to the Outer Planes - places where the infinite magic of the astral has been harnessed to conjure an entire world from the mists.

Belief is the ultimately the only force powerful enough to reshape the Astral and create permanent realms - the belief of thousands or even millions of sentient creatures. These realms, the “continents” of the astral sea, are known as the Outer Planes.

In some cases, the belief required to create an Outer Plane came about organically. If enough mortals believe that there must be a place of punishment that the sinful go to when they die, then one will come to be. More often than not, though, the belief is channeled through a deity - or even an entire pantheon. Outer Planes that have a master are under their complete control; the plane only exists due to a constant exertion of will over the surrounding chaos, so it is trivial to change natural laws or reshape the world on a whim.